In some integrated circuits (ICs), such as the radio frequency front-end modules (RF FEMs), etc., inductors are important electronic devices. The specific parameters of the inductors directly affect the performance of those ICs. In existing technologies, inductors are often planar inductors, such as planar spiral inductors, etc. The planar inductors are formed by winding a metal wire on the surface of a substrate or a dielectric layer. Comparing with conventional coil inductors, the planar inductors have the advantages including low cost, easy integration, low noise and low power consumption, etc. Most importantly, the planar inductors are compatible with existing IC fabrication processes.
FIGS. 1-2 illustrate an existing planar inductor. FIG. 1 is a cross-sectional view of the structure illustrated in FIG. 2 along the AA′ direction; and FIG. 2 is a top view of the structure illustrated in FIG. 1.
The planar inductor includes a semiconductor substrate 100; and a dielectric layer 101 formed on the semiconductor substrate 100. Further, the planar inductor also includes a planar coil 102 formed on the dielectric layer 101.
As shown in FIG. 2, the planar coil 2 is formed by three turns of metal wires. The radius “R” of the most inner turn of the planar coil 102 is in a range of approximately 45 μm˜50 μm. The width “W” of the metal wire of the planar coil 102 is in a range of approximately 8 μm˜10 μm. The planar coil 102 has an octagonal shape. Further, one end of the planar coil 102 has an input contact point 103; and the other end of the planar coil 102 has an output contact point 104. The input contact point 103 and the output contact point 104 are used for current input and output, respectively.
For an inductor, a quality factor Q is used to evaluate its performance. The quality factor Q is equal to a ratio between the energy stored in the inductor and the energy lost during an oscillating period. Thus, the higher the quality factor Q is, the higher the efficiency of the inductor is; and the better the performance of the inductor is. The factors affecting the quality factor Q of an inductor include the inner resistance of the metal line of the coil, the parasitic capacitance between the coil and a metal layer over or below the coil, or the parasitic resistance between the coil and the semiconductor substrate. Specifically, the higher the resistance is, or the higher the parasitic capacitance is, the smaller the quality factor Q is, and the worse the performance of the inductor is.
However, the quality factor Q of the existing planar inductor is substantially low. Further, the fabrication process of the planar inductor has a relatively low integration level with the fabrication processes of other semiconductor devices. Thus, the fabrication process of the planar inductor is relatively complex. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.